The present invention relates to a method of clearing, and therewith releasing, a communication connection established between a mobile station and a mobile radio network that form part of a mobile radio system. The system includes a plurality of mobile stations that are served by the network, and may also include several networks with associated mobile stations. More specifically, but not exclusively, the invention relates to a method of forcing a mobile station to relinquish an allocated radio channel when reception is impaired, so that this channel can be better used by another mobile station in which reception on precisely this radio channel is better. The invention also relates to a mobile station which utilizes the proposed method.
The mobile stations (the mobile telephone sets) of a mobile radio system, for instance a mobile telephone system, normally use a so-called dedicated radio resource as a communications channel when establishing radio communication between the mobile station and the network. By "network" is meant in the following a base station with which the mobile station can communicate directly, and a mobile radio exchange which establishes and executes the fixed connections between a given number of different base stations. The mobile radio exchange is also normally connected to a fixed public switched telephone network (PSTN or ISDN). In the majority of cases, the communications channel assigned to the mobile station is a so-called traffic channel over which speech or data information is transmitted.
When there is no longer any need for this communications channel, the mobile station releases its allocated radio resource, so that this resource can be reused by another user. Since the allocated radio resources (the radio channels) in the medium are scarce in relation to the number of users, it is obviously of great importance that a radio resource which is not utilized to the full or a radio resource which is poorly used by a user quickly becomes available for another user.
Both the allocation of a radio channel to a mobile station, i.e. when the mobile station begins communicating with the network over the allocated channel, and disconnection of the mobile station from the allocated channel, i.e. when the mobile station ceases to communicate over said channel and releases the same, are controlled by signalling between the network and the mobile station.
In the case of cellular and frequency/time division systems, for instance cellular TDMA-systems, it is known to control a normal situation, such as disconnecting the mobile station from the communications channel, in accordance with a signalling procedure between the network and the mobile station; see for instance "DIGITAL CELLULAR TELECOMMUNICATION SYSTEM RCR STANDARD" RCR STD-27A, Version January 1992, Research and Development Center for Radio Systems (RCR), Chapters 4.3.5.2.21-22 and 4.3.8.4.
In this signalling procedure the network sends to the mobile station a signal which commands the mobile station to relinquish the radio resource (the radio channel). When receiving this command signal, but before relinquishing the radio channel, the mobile station sends a signal confirming that the command has been received, and the mobile station relinquishes the radio resource immediately after the confirmation signal has been sent to the network.
Thus, when practicing this signalling procedure, the network is made aware by the mobile station that said station intends to relinquish the communications channel, thereby informing the network that this communications channel can be reused.